We run four 2500mah rechargable AAs where I race but we also use stock HPI motors. We can get between 40mins to an hours worth of run time on a set but after about 30-35mins they deffaintly start to slow down. There is one person who has ran a modified stock motor and it will only last about 3/4 of what ours last so you probably wont get as much run time out of them as we do if you run a faster motor. I run energizers which you can just buy at wall mart.
Duracell has a pack of 4 ni-mh 2650mAh AA cells for $10. That's what I use for my radios. Had them in there for a month, and i've never had to recharge so far.
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Main R/C focus as of right now:
TT-01 for science fair
Don't know if you are racing and have limits to what you can use, but I use Intelect 1400mah 6c SxS packs with an HPI Micro Mod 45T motor and the power is unbelievable. I have never timed the runtime, but usually change bateries after about 30min just out of habit!
I'm not into racing, only with friends at our own private tracks (mine and my neighbours). We ust have a "gentlemen agreement" to use max. 5Cells. My aim is to build a endurance racer based on the 5 cell reglementation.
I used to use 5c pacs and got similar runtimes. I used 1200mah Venom reciever packs that I dismantled and put SxS! Little less speed and power though! I use this car to play with the 1:10 guys!
If your looking for endurance racing then why dont you just get a lithium Ion pack with the stock motor.........should last you a good 30minutes maybe even more.......but as a comparison the aa's dont have the voltage output you need as with a 2/3a pack.